NOAO >   Observing Info >   Approved Programs >   2004B-0313

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Proposal Information for 2004B-0313


PI: George H. Heald, University of New Mexico, gheald@phys.unm.edu
Address: Physics Department, 800 Yale Blvd NE, Albuquerque, New Mexico 87131, USA

CoI: Richard J. Rand, University of New Mexico
CoI: Robert A. Benjamin, University of Wisconsin - Whitewater
CoI: Matthew A. Bershady, University of Wisconsin - Madison

Title: Kinematics of the Disk--Halo Flow in NGC 891

Abstract: The importance of cycling of gas between disks and halos of galaxies is now well established in the evolution of ISMs. While the diffuse ionized gas (DIG) has proven an excellent tracer of disk-halo cycling, only limited information exists on the kinematics of such flows in edge- on spirals. We now have two-dimensional velocity field information for the very active flow in NGC 5775 and for the much less active flow in NGC 4302. However, for the more moderate flow in NGC 891, the best studied example of disk-halo cycling, we have only one long-slit spectrum. Data for NGC 891 and NGC 5775 show that the decrease of rotation speed with height off the plane is less than expected from ballistic models of disk-halo flow, especially for the moderately active NGC 891. These results suggest that (magneto-)hydrostatic/hydrodynamic effects, such as a viscous or magnetic coupling of disk and halo gas, or an outwardly directed radial pressure gradient in the halo, maintain the higher velocities, and that such effects may be more important in spirals with less active flows. Thus the results indicate new physics regarding halo gas support and demonstrate the need for good observational characterization of deviations from ballistic flow. We therefore propose to observe NGC 891 using SparsePak on WIYN to complete a set of 2-d studies of three DIG halo velocity fields. These data will allow us to characterize the importance of these effects both radially and vertically in edge-ons with three levels of cycling activity at comparable sensitivity.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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